1. Field of the Invention
The present invention relates to a printing apparatus, and more particularly to a printer suitable for use in an electronic typewriter having an automatic correction function.
2. Description of the Prior Art
Many types of electronic typewriters have an automatic correction function for automatically correcting a printed character. For example, such a typewriter is shown in U.S. Pat. No. 3,780,846. In such a typewriter, character information is stored in a line buffer memory (such as memory 40 shown in FIG. 1 of U.S. Pat. No. 3,780,846) for the automatic correction function, and the content of the memory is retrieved as required to effect the correction. No character key need be depressed since a correction key need only be depressed to correct the printed character. This system is very convenient to an operator but has the following problem.
For example, assuming that a fraction "1/2" is to be printed. After "1" has been printed in superscript, a dash "--" is printed. In this case, information on the printed "1" stored in the line buffer memory LB (such as memory 40 shown in U.S. Pat. No. 3,780,846) is deleted from the line buffer LB and information on the dash "--" is substituted therefor as shown in FIGS. 1(A) and 1(B). Accordingly, when the characters representing the printed fraction are to be erased, all of the characters of the fraction cannot be erased by one correction key depression but rather must be erased one character at a time by manual operation or other means. This erasing operation is very troublesome and time-consuming.
When a composite character such as "Y" is to be printed, "Y" is printed and then "=" is overprinted. In this case, character information on the printed "Y" stored in the line buffer LB is deleted when "=" is printed and character information on "=" is substituted therefor. As a result, it is not possible to simultaneously erase the characters "Y" and "=" of the composite character "Y" by depression of the correction key, and the non-erased character must be erased by other means. Again, this erasing operation is trouble-some and time-consuming.